This invention relates to an oriented fiber composite structure adapted for use in a wide variety of sealing and load transfer applications and to a method and apparatus for making same. A material having two or more distinct constituent materials is a composite material. Composite materials consist of one or more discontinuous phases embedded in a continuous phase. The discontinuous phase is usually harder and stronger than the continuous phase and is called the REINFORCEMENT, whereas the continuous phase is termed the MATRIX. A composite material is produced when the volume fraction of the reinforcement exceeds ten percent and when the property of one constituent is at least five times greater than that of the other. Composite materials characteristically exhibit significant property changes as a result of the combination of reinforcement and matrix materials.
Fiber Reinforced Plastic (FRP) composite structures belong to one of two categories, depending upon whether or not the fiber reinforcement constituents are tensioned during fabrication of the composite structure. One category to which FRP composite structures belong is referred to as the Loose Fiber Reinforced Plastic (LFRP) category. The LFRP composites include those fabricated from chopped strand fibers, random oriented fiber mat, surfacing veil, felt-like fabrics, milled fibers or woven cloth. The other category is referred to as the Tensioned Filament Reinforced Plastic (TFRP) category. The TFRP composites include those fabricated from continuous unidirectional filament strands which are collimated, oriented and tensioned during the fabrication process. The TFRP composites are made by the pultrusion method, by the filament winding method, or by the combination of these two methods known as the "LONGO-CIRC" method. Pultruded TFRP composites include those containing continuous unidirectional collimated filament reinforcements which are tensioned while the filaments are pulled through extrusion dies which form the composite into structural shapes, such as angles or tees, of nearly any length. Pultruded composite structures primarily comprise tensioned "LONGOS", the name given by the American Society of Mechanical Engineers (ASME) in Section X of the Boiler and Pressure Vessel Code to longitudinally oriented filament reinforcements. Filament wound composites, on the other hand, primarily consist of tensioned "CIRCS", the ASME name given to circumferentially wound filament reinforcements. This invention includes the class of TFRP composites which contain both LONGOS and CIRCS and particularly tubular laminate structures fabricated in accordance with the "parabolic tensioning" methods taught by U.S. Pat. No. 3,784,441. The tubular laminate structures described by the specifications and illustrations of the present invention are ideally suited to serve as pipe, truss and tank structures and can resist internal pressure loads and the longitudinal and circumferential stresses which are simultaneously imposed upon the tubular laminate plies.
Prior art methods for joining tubular filament wound laminates subjected to longitudinal stresses have a joint bond strength that can never exceed the interlaminate shear strength of the plastic matrix material used to bond the laminate plies and their constituent filament reinforcements. The longitudinal loads transferred through bolted flanges, threaded ends and other prior art mechanical methods used to join and disconnect tubular laminate structures are limited by the shear strength of the adhesive material used to bond the flanges, threads or other joint making structures to the end portions of the tubular laminate. The shear strength limitations characterizing plastic matrix or bonding material, restrict, if not prevent, the use of prior art tubular laminate structures to applications where high strength mechanical joints are required. Prior art methods employed to mechanically join and seal tubular laminate structures include threaded ends and flanged ends. Threaded ends used to mechanically join and seal composite pipe of reinforced plastic are generally weaker and less wear resistant than composite flanged-ended counterparts of equivalent size and service. For this reason flanged ends are commonly employed to mechanically join and seal prior art tubular laminate structures which are highly stressed. Such flanges are frequently fabricated as separate structures which are bonded to specially prepared end portions of the composite tubes. Other flanges are filament wound or otherwise formed directly upon ends as an integral part of the composite tube structure. Prior art methods which employ these types of threaded or flanged ends to mechanically join and seal tubular laminate structures are limited by the interlaminate shear strength of the plastic matrix material used to fabricate threaded or flanged laminate structures or by the shear strength of the adhesive material used to bond prefabricated threaded or flanged structures to the ends of tubular laminate structures. For this reason prior art composite structures which mechanically join and seal tubular laminate structures possess a longitudinal tensile end-load resistance capability which is governed by flange thickness, thread root section area or the adhesive surface area employed in bonding the joint structure rather than upon the thickness of certain tubular laminate plies.
Panel laminate structures fabricated in accordance with specifications outlined in the present invention are ideally suited to serve as easily assembled integral elements of monolithic wall or roof structures. Prior art methods for joining flat or curved composite laminate panels generally involve bonding, clamping, riveting or bolting the panels. The prior art panel joining methods prevent the joint strength to equal a panel's maximum tensile and bending strength. This is because the strength of bonded or clamped joints is limited by the interlaminate shear strength of the adhesive material bonding the laminate plies. The strength of bonded and clamped joints is especially diminished when panel joints are flexed or twisted in a manner which imposes peel stresses upon the adhesive bonding material. The strength of bolted or riveted panel joints, although possibly superior to bonded joints, is limited by the tear out, bearing or crush strength of the laminate composite material. These prior art panel joining methods do not enable panel joints to be made which are flush with the joined panels.